1. Field of the Invention
The present invention relates generally to external counterpulsation cardiac assist, and more particularly, to a patient support for use with external counterpulsation cardiac assist.
2. Prior Art
In external counterpulsation cardiac assist device (APPLICATOR) applicators (hereinafter “applicator”) of the prior art, the limb pressure is generated by inflating balloon-like chambers that surround the limb. In addition, to keep the volume of the inflow air in check, the balloon-like chambers are encased in a relatively inextensible fabric to minimize the bulging out of the applicator assembly. A cross-section of a typical such arrangement is illustrated in FIG. 1.
The applicator 100 (alternatively referred to as an actuator) is used by laying the patient on a bed, “wrapping” the applicator around a limb or other body portion 101 (such as the legs, thighs, arms, or buttocks) and affixing the outer liner 104 by Velcro or other similar means such that the assembly stays tightly over the limb 101. The applicators are generally constructed with an inner layer 102 and a relatively inextensible outer layer 104. Between the inner and outer layers 102 and 104, balloon-like members 106 are positioned. The balloon like members 106 are typically made from an elastic material and provide inner cavities or chambers. The applicator operates by pressurizing the balloon-like members 106 with air or other gases through an inlet and/or outlet 108, preferably in synchronization with the patient's cardiac cycle.
Part of the limb 101 such as ankles, knees, feet, elbows, chest area, neck and the head are not covered since due to the absence of a considerable amount of muscle mass, no significant amount of blood can be displaced by the external pressure by the applicators. In the applicators of the prior art, the patient's leg, thighs, arms and buttock are supported by the outer layer 104 over the bed or table (collectively referred to herein as a tabletop). As the result, as the air pressure builds up in the chamber 106, the outer layer 104 has a tendency to bulge out, thereby lifting the limb 100 above the top surface of the tabletop. This is the case even though relatively inextensible outer applicator layers are commonly used which make them resist radial extension but cannot prevent longitudinal bulging of the applicators. The aforementioned lifting following the pressurization of the applicator is illustrated in FIGS. 2a and 2b. FIG. 2a illustrates the applicator during an evacuation cycle in which the chamber 106 is evacuated and FIG. 2b illustrates a pressurization cycle on the right in which the chamber 106 is pressurized with air or any other suitable gas. As can be readily appreciated from the comparison between FIGS. 2a and 2b, the pressurization of the chamber 106 results in a lifting of the limb 100 by an amount H.
Appreciating that the applicator can operate at up to one cycle per heart beat cycle, i.e., in the order of about 60-80 times a minute, and that each time the patient's limb(s) 101 is effectively thrown up a considerable distance (H) above the top surface 112 of the tabletop 110, the discomfort facing the patient becomes apparent. In fact, the length of time that the procedure can be continued is very much related to how long the patient can tolerate such highly stressful and rapid lifting, without excessive and harmful fatigue. In addition, patients also tend to tighten their muscles due to such rapid lifting, thereby reducing the effectiveness of the entire procedure.
A need therefore exists for means to alleviate patients from the stress and other harmful effects of the aforementioned lifting actions during the procedure.